Currently available high-voltage, fluid-filled power transformers utilize cellulose-based insulation materials that are impregnated with dielectric fluids. More specifically, such insulation systems include cellulose-based materials that are positioned between turns, between discs and sections, between layers, between windings and between components at high voltage and ground potential parts (e.g., cores, structural members and tanks).
In order to operate, currently available transformers typically include insulation materials that have a moisture content of less than 0.5% by weight. However, since cellulose naturally absorbs between 3 and 6 weight percent of moisture, a relatively costly process of heating under vacuum is typically performed before cellulose is suitable for use in a power transformer. Even pursuant to such a heating/vacuum process, as the cellulose ages (i.e., degrades over time), moisture eventually forms, as does acid, which accelerates the aging process.
Since the rate at which cellulose ages is dependent upon temperature, normal operating temperatures of currently available power transformers is 105° C. or less. For the same reason, the maximum operating temperature of such transformers is 120° C. or less. As more power is transferred, the higher losses due to higher current generate higher temperatures. As such, cellulose-based insulation systems limit the operational efficiency of power transformers.